Heartbeat rate monitoring

ABSTRACT

Apparatus for monitoring the heartbeat rate of a patient comprising deriving, with pulse forming circuitry, electrical signals representative of heartbeat activity on a beat-to-beat data basis, a gating unit for normally passing the electrical signals, a first unit analyzing three successive ones of the electrical signals by a pair of credence checkers each having a preselected frequency tolerance to define a first criterion for distinguishing valid data and artifact and inhibiting operation of the gating unit upon detection of artifact, and a storage unit for receiving and averaging valid data over a period of three successive heartbeats to provide an output indicative of heartbeat rate. A second analyzing unit compares the third one of said signals with the last passed good data to define a second criterion for distinguishing valid data and artifact and upon detection of valid data inhibiting any effect on the gating unit by the first analyzer unit. Passed values are averaged and displayed and a visible indication denotes occurrence of an artifact.

United States Patent [191 Hatke Dec. 25, 1973 HEARTBEAT RATE MONITORING[57] ABSTRACT [75] Inventor: Fred Louis Hatke, Skillman, NJ.

[ Assigneer nfiffmann'La Roche y, A aratus for monitoring the heartbeatrate of a pa- PP tient comprising deriving, with pulse formingcircuitry, [22] Filed July 13 1972 electrical signals representative ofheartbeat activity on a beat-to-beat data basis, a gating unit fornormally PP 271,307 passing the electrical signals, a first unitanalyzing Related us. Application Data three successive ones of theelectrical signals by a pair [63] C f S N of credence checkers eachhaving a preselected fregy emu-pan 0 quency tolerance to define a firstcriterion fordistinguishing valid data and artifact and inhibitingopera- [52] us Cl 128/2 05 T 128/2 05 Z tion of the gating unit upondetection of artifact, and [51] Int A6lb'5/02 a storage unit forreceiving and averaging valid data [58] Fieid P 2 05 R over a period ofthree successive heartbeats to provide A 06 06 an output indicative ofheartbeat rate. A second analyzing unit compares the third one of saidsignals with the last passed good data to define a second criterion 56 II 1 N References cued for distinguishing valid data and artifact andupon de- U [TED STATES PATENTS tection of valid data inhibiting anyeffect on the gating 3.5 05 7/1971 Thomas et a1... 12 0 A unit by thefirst analyzer unit. Passed values are aver- :EW ie aged and displayedand a visible indication denotes er OVItSU 3.524 442 8/1970 Horth128/206 A ocurrence of an arufact.

Primary Egzminer-William E. Kamrn 7h 4 Claims, 4 Drawing FiguresAtzorneySamuel L. Welt et al. W

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HEARTBEAT RATE MONITORING CROSS-REFERENCES TO RELATED APPLICATIONS It isnoted that this application is a continuation-inpart of application Ser.No. 205,948, filed Dec. 8, 1971, entitled l-IEARTBEAT RATE MEASURINGTECHNIQUE.

BACKGROUND OF THE INVENTION The present invention relates generally toelectrical signal processing techniques for accurately ascertaining theheartbeat frequency of a patient for monitoring purposes.

In the field of heart rate monitoring, numerous problems are incurred inproviding an accurate heart rate for the reason that electrical artifactimpulses indicative of noise or multiple heart signals within a singleheartbeat may be erroneously judged as part of the heart rate count. Incertain applications, i.e., in detecting and analyzing a fetalheartbeat, artifact signals are often generated as a result of thedisturbances introduced by the changing fetal positions and mothermovements including pressure changes caused by labor, to frequentlyproduce two or even three signals per fetal heartbeat. The latter iseven more likely to occur when ultrasound is utilized as the vehicle formonitoring the heart rate, for the reason that the reflections of theultrasound might occur in response to not only movement of the front andback wall of the heart but in response to the heart valves and othermotions about the fetal site.

As a consequence of these artifact problems, errors are often introducedin the counting of the heart signals and/or sounds, and might lead to anincorrect diagnosis giving rise to needless emergency measures in someinstances or obscuring the need for emergency measures in otherinstances.

SUMMARY OF THE INVENTION Accordingly, it is the purpose of the presentinvention to avoid suchproblems as those noted above by provision of anelectrical signal processing technique that evaluates or analyzes thesignal corresponding to at least three successive heart beats based onpreselected frequency tolerance criteria as a first step to distinguishvalid data from artifact and in addition anaylyzes the third one of saidheart sounds with the last piece of valid data, to further ascertain thevalidity of each heart activity signal and ignore artifact.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a scanningsystem in which the present invention is employed.

F lG. 2 is a voltage versus time graphic representation of the nonlinearhyperbolic signal generated by the function generator 23, shown in FIG.1.

FIG. 3 is a schematic diagram of the credence checker 32 or 33illustrated in FIG. 1.

FIG. 4 is a waveform diagram showing the operation on a certain inputsignal to the system shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there isshown a transmitting transducer 11 driven by generator 12 fortransmitting ultrasonic energy to a fetus, roughly illustrated as 13,

within the maternal abdomen. The ultrasonic energy transmitted to thebody may be of the pulsed wave or continuous wave type. Although anultrasonic system is illustrated at the front-end, it is readilyunderstood that the present invention can be similarly employed withphonocardiographic or electrocardiographic techniques. A receivingtransducer 14, adapted for deriving electrical impulse signals respondsto the ultrasonic signals returned from the fetus 13. The receivingtransducer 14 is connected to a mixer 15. Mixer 15 which is alsoconnected from generator 12, amplifies the incoming signals and mixesthem to provide a resultant Doppler signal output.

As was previously discussed, the output of the mixing unit 15 comprisinga waveform complex, similar to a phonocardiographic output orelectrocardiographic output, which includes a multitude of signals. Theoutput signals from mixer 15 are processed by a conditioning unit 16including a bandpass filter having a frequency range anywhere, forexample, between cycles and 400 cycles, and a pulse shaper for providingDoppler pulses of a uniform pulse width as, for example, ms. which isequivalent to about 5 V2 heartbeats per second. If desired, the bandpassfilter output might be connected to an audio amplifier (not illustrated)for driving earphones or a recorder. The conditioning unit 16 isconnected to four one shot multivibrator units 18, 19, 21 and 22connected in cascade and each being triggered for a period of 5 ms.except for one shot unit 22 which is triggered for a period ofapproximately 44.68 ms.

A function generator 23 connected from one shot 22, is adapted togenerate a hyperbolic function approximation having an RC exponentialdecay as illustrated in FIG. 2, to decrease from the maximum of 6 voltsto, for example, 0.6 volts at I second. The function generatorcapacitance begins charging up at the leading edge of the signalgenerated by one shot unit 22 and is held at the 6 V potential untilreleased at the trailing edge. The function generator is made so thateach point along the hyperbolic curve is indicative of a potential valuerepresenting a selected heart rate on a beat-tobeat basis. This similarfunction may also be achieved by utilizing a digital counter. At theleading edge of the next successive pulse generated by one shot 22 thepotential value to which the exponential curve has decayed willrepresent a heart rate value determined by the time duration between twoconsecutive leading edges of pulses generated by one shot 22.

Function generator 23 is connected -to a sample and hold unit 24 viaswitch 24', thence to a sample and hold unit 25 via switch 25' andthence to a sample and hold unit 26 via switch 26. Sample and hold unit24 is also connected to a credence checker 40 and to a sample and holdunit 27 via switch 27', thence to a sample and hold unit 28 via switch28', and thence to a sample and hold unit 29 via switch 29'. All threeof the sample and hold units 27, 28 and 29 are connected throughseparate resistors to an output unit 31 which is provided to indicate anaverage of the signals held in sample and hold units 27, 28 and 29.

Sample and hold units 24 and 25 are further connected to a credencechecker 32, and sample and hold units 25 and 26 are connected to acredence checker 33. The credence checkers 32 and 33 act as comparatorsin that they are adapted to produce an output if the difference betweentheir inputs are separated by more than a predetermined allowable limit.An example of the credence checker unit is illustrated in FIG. 3 whereinresistors 34 and 35 are adjustable to set the variable credence criteriaselected. The input on lead 36 fed via resistors 34 might, for example,be from sample and hold unit 24 and the input on lead 27 fed viaresistors 35 might, for example, be from the sample and hold unit 25.The inputs on leads 36 and 37 are compared at an operational amplifier38. Should the input on lead 36 or lead 37 fall outside the potential onlead 37 or lead 37 by i A V where A V is the predetermined allowablelimit, an output from amplifier 38 will appear across output loadresistor 41. If V 36 is greater than V 37 A V then transistor 39 willconduct, however, should V 36 be less than V 37 A V, transistor 42 willconduct. In the present embodiment one might use, for example thecriteris :L 20 beats per minute as the predeterm inedallowable. limit.

With reference back to FIG. 1, credence checkers 32 and 33 are eachconnected to a NOR gate 43 which is inhibited upon an output generatedfrom either or both of the credence checkers. NOR gate 43, in turn, isconnected to a gate 44, which is also connected from the one shot unit22 in such a manner that gate 44, will only pass the output of one shot22 in the absence of an output from NOR gate 43, or, in effect, in theabsence of outputs from either of the credence checkers 33 or 32. Thegate 44 output controls the switch 27 which is normally open at theinput to sample and hold unit 27.

The third credence checker 40, connected from sample and hold unit 24and output sample and hold unit 27, is coupled to NOR gate 43 in such amanner as to inhibit NOR gate 43, if the credence test based on apredetermined frequency tolerance is positive indicating that thedifference frequency between its inputs fall within the prescribedfrequency limits. Similar to credence checkers 32, 33, the frequencytolerance might use a criteria of i 20 beats per minute as apredetermined allowable deviation limit on a beat-to-beat basis. Themanner of inhibiting NOR gate 43 may be accomplished by grounding itsoutput lead through activation of an otherwise normally open switch 40'.

Switches 28 and 29 are respectively controlled by the outputs of oneshot units 19 and 18. With reference back to NOR gate 43, this gate isalso connected to a normally closed switch 45 which normally grounds anAC source, for example, the 60 cycle line input, being passed viaresistor 46. Otherwise, with switch 45 open the AC source input will befed via capacitance 47 via output unit 31, which will be fed to arecorder or other similar display unit.

OPERATION With reference to FIGS. 1 and 4, typical processing circuitrywill condition the Doppler signals to provide uniform duration pulsesof, for example, I80 ms. in the present embodiment as is illustrated inFIG. 4-a. Accordingly, the leading edge of each alleged heartbeat signalwill trigger one shot 18 to provide a ms. output shown in FIG. 4-b whichtrailing edge in turn, generates a second 5 ms. signal from one shot 19as shown at FIG. 4-c, again, its trailing edge generates yet a third 5ms. pulse from one shot 21 as is illustrated at FIG. 4-d. The trailingedge of the pulse from one shot 21, in turn, triggers one shot 22 togenerate a 44.68 ms. pulse causing at the leading edge, the capacitor ofthe function generator to charge up to the 6 volt level and be held atthat level until the duration of the 44.68 ms. period. At the trailingedge of the one shot 22 pulse, the capacitor of the function generator23 begins to discharge along the hyperbolic curve displayed in FIG. 2.

Upon occurrence of the next Doppler pulse or alleged heartbeat whichgenerates yet another pulse at one shot 22, the function generator willagain be charged up. However, during the 5 ms. period immediatelypreceding the second triggering of one shot 22, one shot 21 will closegate 24 causing the function generator to be sampled and providing asignal at the sample and hold unit 24. This signal represents apotential which is proportional to the heart rate on a beat-tobeatbasis. In a similar manner, as one shot 18 and one shot 19 aretriggered, sample and hold units 26 and 25 willaccept signals being heldat the sample and hold gates 25 and 24 respectively, as gates 26' and25' are temporarily and consecutively closed.

The signals present in sample and hold units 24 and 25 are compared atcredence checker 32, and similarly, the signals in the sample and holdunits 26 and 25 are compared to the credence checker 33. Assuming thecriteria at each of the credence checkers 32, 33 and 40, is notexceeded, no output, as represented at FIG. 4-f, will appear on the leadlines to the NOR gate 43 in which case NOR gate 43 will remain on topass the pulse signal generated by one shot 22 through the gate 44 toclose switch 27'. Assuming the criteria at credence checker 40 is alsonot exceeded, the NOR gate 43 input to gate 44 is grounded to ensureclosing of switch 27 and passing of the latest pulse signal from oneshot 22, irrespective of the output of credence checkers 32, 33. Uponthe closing of switch 27 the signal from sample and hold unit 24 isreceived at the sample and hold unit 27. During the next cycle, thesignal at sample and hold unit 27 is transferred to sample and hold unit28 upon the triggering of one shot 19.

In a similar manner, the sample and hold unit 29 will receive the signalfrom sample and hold unit 28 upon the triggering of one shot 18 duringthe next successive cycle. The signals in sample and hold units 27, 28and 29 are added via their output resistors by an output unit 31 whichis adapted to take the average of these three signals whereby theaverage signal is displayed on, for example, a chart recorder, a digitalvolt meter, or an analogue volt meter.

Assuming, for example, that as to any cardiac signal the credencechecker 32 indicates that, for example, the beats per minute per beatmight exceed 20 cycles positive or negative as is illustrated at FIG.4-g, NOR gate 43 is inhibited (see FIG. 4-h). Gate 44 will thereforeinhibit the pulse passing from one shot 22 (see FIG. 4-1') therebyleaving switch 27' in its normally opened position so as not to acceptthe signal from the sample and hold unit 24 since it has been indicatedby credence checker 32 that this signal appears to be an inaccurate one.With this interruption of the flow of data to the sample and hold unit27 by occurrence of an artifact signal the last previous piece of validinformation in sample and hold unit 27 will be maintained andtransferred additionally through to the next sample and hold unit 28.

To indicate that new input signals have been rejected as artifact whenthe predetermined credence criteria has not been met and that theaverage heart rate is made on the sample of only two as opposed to threesuccessive signals, the inhibiting of NOR gate 43 will also cause thenormally closed switch 45 to be opened. In such circumstance, the ACsource input which is normally grounded will be fed via capacitor 47 tothe input unit 31. This additional output allows some of the AC sourcesignal to be applied to the output causing the resultant pen and inktrace, in the case of a chart recorder, to be widened to visiblyindicate artifact. This, in effect, provides a review of the immediatelyprevious heartbeat rate with an indication that the credence criteriahave not been met by the latest heartbeat signals and that some problemmay exist.

It may be observed from the above, that absent credence checker 40,credence checkers 32, 33 would require at least three consecutive beatsto be within the tolerance of the credence system before any inputsignal is allowed to be transferred to the output sample and hold unit27. Although such an arrangement provides fairly reliable results, it isexpedient to provide a credence check 40 which compares the newest datain sample and hold 24 with the last good valid in sample and hold 27. Ifthis latter test fails, in that the tolerance is exceeded, the output ofNOR gate 43 is allowed to function normally, that is, should either orboth credence check units 32 or 33 fail, NOR gate 43 inhibitsapplication of the newest data via gate 44 to the sample and hold unit27, and broadening of the pen/ink trace and/or an acoustical or opticalalarm is excited. However, if the test of credence check unit 40 ispassed, to indicate that the newest data in sample and hold 24 and thelast piece of valid data in sample and hold 27 are within tolerancelimits, then the decision is made that the newest data in sample andhold 24 is good and should be passed to sample and hold unit 27 in whichcase NOR gate 43 is inhibited from being actuated by either of thecredence check units 32, 33 in case either or both should be energizedby virtue of exceeding tolerance limits. The advantage by includingcredence check unit 40 allows the newest data which is valid to bepassed to the sample and hold unit 27. Otherwise valid data is notpassed to the sample and hold unit 27 until artifact has cleared sampleand hold units 25 and 26 taking a duration of three heartbeats. Thisaddition, in effect, reduces the number ofartifact indications.

I claim: 1. Apparatus for monitoring the heartbeat of a patientcomprising:

means for deriving electrical signals representative of heartbeatactivity on a beat-to-beat data basis;

gating means for normally passing said electrical signals and actuableto inhibit the passing of selected one(s) of said signals;

first analyzing means for selectively comparing three consecutive onesof said electrical signals to define a first criterion fordistinguishing valid data and artifact and actuating said gating meansupon detection of artifact,

output storage means for receiving and averaging valid data over aperiod of three successive heartbeats to provide an output indicative ofheartbeat rate;

second analyzing means for comparing the third one of said signals withthe last passed valid data to define a second criterion fordistinguishing valid data and artifact and upon detection of valid datapreventing actuation of said gating means by the first analyzer means.

2. Apparatus according to claim 1 wherein said first analyzer meanscompares within a predetermined frequency tolerance a first and secondone of said signal values and the second and a third one of said signalvalues.

3. Apparatus according to claim 2 wherein said second analyzer meansmakes a comparison within a predetermined frequency tolerance.

4. Apparatus according to claim 1 including indicator means energizedupon actuation of said gating means for indicating the detection ofartifact.

1. Apparatus for monitoring the heartbeat of a patient comprising: means for deriving electrical signals representative of heartbeat activity on a beat-to-beat data basis; gating means for normally passing said electrical signals and actuable to inhibit the passing of selected one(s) of said signals; first analyzing means for selectively comparing three consecutive ones of said electrical signals to define a first criterion for distinguishing valid data and artifact and actuating said gating means upon detection of artifact, output storage means for receiving and averaging valid data over a period of three successive heartbeats to provide an output indicative of heartbeat rate; second analyzing means for comparing the third one of said signals with the last passed valid data to define a second criterion for distinguishing valid data and artifact and upon detection of valid data preventing actuation of said gating means by the first analyzer means.
 2. Apparatus according to claim 1 wherein said first analyzer means compares within a predetermined frequency tolerance a first and second one of said signal values and the second and a third one of said signal values.
 3. Apparatus according to claim 2 wherein said second analyzer means makes a comparison within a predetermined frequency tolerance.
 4. Apparatus according to claim 1 including indicator means energized upon actuation of said gating means for indicating the detection of artifact. 